This invention relates to lift trucks and, more particularly, to overload moment sensing systems for use in lift trucks.
Prior art of possible relevance includes U.S. Pat. No. 2,751,994 of June 26, 1956, and U.S. Pat. No. 2,774,437 of Dec. 18, 1956, both to Remde; U.S. Pat. No. 3,032,221 of May 1, 1962 to Carliss et al; U.S. Pat. No. 3,831,492 of Aug. 27, 1974 to Young; U.S. Pat. No. 3,850,323 of Nov. 26, 1974 to Eckstrom; and U.S. Pat. No. 3,866,419 of Feb. 18, 1975 to Paul.
Lift trucks have increased greatly in popularity due to their maneuvering ability and load carrying capacity. As is well known, the typical lift truck includes a mast pivoted to the front end of the vehicle for fore and aft tilting movement thereon. A carriage is provided with a fork or the like and is mounted for up and down movement on the mast and hydraulic cylinders are employed for both tilting the mast and elevating the carriage.
Because the load is carried forwardly of the front wheels of the vehicle, increased loading on the platform increases the tendency of the lift truck to become overloaded in its forward direction.
Various means have been provided for warning the operator of a lift truck of an overload condition and/or for varying the operation of the lift truck to preclude an overload condition from occurring. The above identified prior art typifies the approaches taken.
One significant difficulty in many of the approaches is the use of valves responsive to pressure variations. Because such elements necessarily are mechanical in nature, sticking of the valves or other causes of mechanical failure can render such systems inoperative.
In addition, many are designed in such a way that an overzealous operator can, if desired, override the system to create a situation which the system was designed to prevent.